1. Field of the Invention
The present invention relates to a pattern recognition apparatus for recognizing an input signal and, more particularly, to a pattern recognition apparatus suitable for implementation of an integrated circuit.
2. Description of the Related Art
FIG. 1 is a block diagram showing a conventional arrangement of a speech recognition apparatus as one type of pattern recognition apparatus. A voice signal input by a voice signal input means such as microphone 10 is supplied to acoustic analysis section 11. In section 11, voice features such as frequency spectra are analyzed in units of predetermined frame lengths (normally, several ms to several tens of a ms), and feature data is time-serially extracted. The time-series data is stored in memory device 12, and a word boundary, i.e., start and end points of an effective voice is detected by word boundary detection section 13. The start and end points of the effective word detected by section 13 are supplied to address table 14 of memory device 12. Based on an output address from the address table 14, a data string in a specific voiced period or with a set of word boundaries is fetched from memory device 12 as recognition data, and is supplied to similarity computing section 15.
Reference pattern memory device 16 stores a large number of reference pattern data. Similarity computing section 15 performs similarity computation between these reference pattern data and the data strings fetched from memory device 12. The computation result is supplied to determining section 17, and voice data corresponding to the reference pattern having the maximum similarity is output as a recognition result.
A word period duration when the reference pattern data is stored in memory device 16 does not often coincide with an input word period duration to be recognized. For this reason, when data to be recognized is fetched from memory device 12, the fetched data is time-serially normalized in correspondence with the duration of the reference pattern data, and then, the similarity computation must be performed.
Various time-series normalizing methods of input pattern data have been proposed. However, these methods must use complicated apparatuses, and a high recognition accuracy cannot be obtained.